Two ACL regions that are configured by the driver during initialization are
the ones used for IPv4 and IPv6 multicast forwarding. Entries residing
in these two regions match on the {SIP, DIP, VRID} key elements.

Currently for IPv6 region, 9 key blocks are used:
* 4 for SIP - 'ipv4_1', 'ipv6_{3,4,5}'
* 4 for DIP - 'ipv4_0', 'ipv6_{0,1,2/2b}'
* 1 for VRID - 'ipv4_4b'

This can be improved by reducing the amount key blocks needed for
the IPv6 region to 8. It is possible to use key blocks that mix subsets of
the VRID element with subsets of the DIP element.
The following key blocks can be used:
* 4 for SIP - 'ipv4_1', 'ipv6_{3,4,5}'
* 1 for subset of DIP - 'ipv4_0'
* 3 for the rest of DIP and subsets of VRID - 'ipv6_{0,1,2/2b}'

To make this happen, add VRID sub-elements as part of existing keys -
'ipv6_{0,1,2/2b}'. Note that one of the sub-elements is called
VRID_ROUTER_MSB and does not contain bit numbers like the rest, as for
Spectrum < 4 this element represents bits 8-10 and for Spectrum-4 it
represents bits 8-11.

Breaking VRID into 3 sub-elements makes the driver use one less block in
IPv6 region for multicast forwarding. The sub-elements can be filled in
blocks that are used for destination IP.

The algorithm in the driver that chooses which key blocks will be used is
lazy and not the optimal one. It searches the block that contains the most
elements that are required, chooses it, removes the elements that appear
in the chosen block and starts again searching the block that contains the
most elements.

When key block 'ipv4_4' is defined, the algorithm might choose it, as it
contains 2 sub-elements of VRID, then 8 blocks must be chosen for SIP and
DIP and we get 9 blocks to match on {SIP, DIP, VRID}. That is why we had to
remove key block 'ipv4_4' in a previous patch and use key block that
contains one field for VRID.

This improvement was tested and indeed 8 blocks are used instead of 9.
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>